The conventional reciprocating piston-type internal combustion engine commonly used in automotive vehicles can be significantly improved if part load throttling and friction losses are reduced. In other words, conventional engines of this type are designed such to give optimum performance at full load, wide open throttle. At less than wide open throttle, and particularly at the lower speeds, the fuel in the combustion chamber of any fixed stroke engine will be less dense. Consequently, its burning efficiency will be reduced. Further, the friction losses in a reciprocating piston-type engine remain relatively constant regardless of speed. Consequently, at the lower speeds, the friction losses are a greater proportion of the work being expended to require the performance output. Lower throttling and friction losses will provide reduced fuel consumption, i.e. greater fuel efficiency. Further, the resulting improvement in fuel efficiency can be additionally enhanced by concurrent optimization of the compression ratio for each engine displacement.
Variable stroke piston engines are known, such as shown for example in the following U.S. patents: U.S. Pat. Nos. 1,112,832; 1,189,312; 1,372,644; 2,653,484; 2,873,611; 2,909,163; 4,131,094; and 4,538,557.
In certain of the systems, for example, as shown in U.S. Pat. No. 2,909,163, an articulated linkage is provided between the crankshaft pin and the piston connecting rod that allows for varying the piston stroke while maintaining a constant piston clearance with the cylinder head (as is useful in compressor applications), or varying the piston clearance with each change in piston stroke. Adjustment of the stroke is effected manually on the exterior of the engine block or frame.
Manual adjustment is common to the remaining aforementioned patents with the exception of U.S. Pat. No. 4,131,094 wherein there is shown a system for automatically adjusting the piston stroke in accordance with different density of the fuel-air charges to be inducted into the combustion chamber.